In the description of the related art and the description of the invention, the correlation between components denoted by the same reference numerals does not indicate that the configurations and functions thereof are the same, but merely indicates a partial correlation in function or general design. Even when specific configurations or functions are significantly different, the same reference numerals may be used.
Various atmospheric dust is produced in manufacturing processes and consumers activities. Among them, dusts with a diameter of more than approximately 10 μm is called dustfall, which can present in the atmosphere in a free-falling status. Dustfall is a significant environmental problem, and investigations and countermeasures need to be put in place. In order to determine the true dustfall situation, it is important to accurately measure the amount of dustfall. Therefore, a device for accurately trapping dustfall is needed.
Comparatively large particles in the atmosphere, for example, dustfall which has particles having a diameter of more than 10 μm, do not completely follow the ambient atmospheric flow, and fall in the atmosphere at a different speed in accordance with the density or the size of the particle of the dustfall to be deposited on the ground. When there is a barrier in the atmosphere, the dustfall collides with the barrier and adheres thereto. For this reason, the environmental influence of the dustfall mainly occurs due to pollution caused by the dustfall deposited and adhering to a specific object. Therefore, in order to evaluate the environmental influence of the dustfall, a simple measurement of the concentration of the dustfall in the atmosphere is not sufficient, and the amount of dustfall passing through a unit area of an inspection surface fixed in a space per hour, that is, the flux of the dustfall needs to be measured.
The flux of the dustfall which is the cause of environmental problems may be divided into a vertical flux and a horizontal flux. In the vertical flux, the inspection surface is horizontal, and is mainly in relation to the evaluation of the deposition of the dustfall on the ground. In the horizontal flux, the inspection surface is vertical, and mainly relates to the evaluation of the adherence of the dustfall to a vertical surface such as a wall of a building. The atmospheric flow outside a building, that is, wind may be regarded as having a vector in the horizontal plane according to an average for a long period of time. For this reason, the vertical flux is not influenced by the wind speed. In contrast, the horizontal flux is a function of the wind speed. More specifically, the flux of the dustfall may be defined by the following equation.[vertical flux of dustfall]=[concentration of dustfall]×[falling speed of dustfall][horizontal flux of dustfall]=[concentration of dustfall]×[wind speed of vertical component of inspection surface]
Likewise, in order to measure the horizontal dustfall flux, there is a need to recognize the wind direction or the wind speed during measurement at all times. Furthermore, the measurement device needs to have a function of trapping the flow of the dustfall in the wind direction at all times. On the other hand, in the measurement of the vertical flux of the dustfall, such consideration is not needed, and the horizontal dustfall flux may be measured in a simpler manner. For this reason, in the public management of the dustfall, a device solely measuring the vertical flux, for example, a deposit gauge shown in FIG. 1 has been used. In the deposit gauge, a dust sampling port 1 is formed in a trumpet shape which is opened upward. The dustfall is trapped in a manner such that the dustfall falling and deposited on the inner surface of the dust sampling port 1 is made to flow into a trap container 25 present below the dustfall sampling port 1 by rainwater or water used for collecting the trapped dustfall.
Further, the horizontal dustfall flux may be formally transformed from the vertical flux in the following equation.[horizontal flux of dustfall]=[vertical flux of dustfall]×[wind speed of vertical component of inspection surface]/[falling speed of dustfall]
Here, the wind speed of the vertical component of the inspection surface is defined as below. First, an imaginary inspection plane is vertically installed at a point which causes a problem. At this time, the wind speed of the vertical component of the inspection surface is a component in accordance with the direction perpendicular to the inspection plane in the wind speed at the point.
For this reason, even when the horizontal dustfall flux is regarded as a problem, a simple evaluation using the measurement result of the vertical flux and the equation has been conducted. However, in fact, it is difficult to quantitatively measure the falling speed of the dustfall variously changing with time, and a large error occurs when calculating the horizontal dustfall flux on the basis of the equation. Therefore, when the horizontal flux is a problem, it is desirable to directly measure the horizontal flux from the viewpoint of measurement precision. In order to directly measure the horizontal dustfall flux, generally, a method is known in which a horizontal component of dustfall is trapped by a certain trapping device and the trapped amount is converted into a horizontal dustfall flux by using values of the trap time, the opening area of the trapping device, and the like.
Here, the horizontal dustfall component amount will be described. The form of adherence (deposition) of the dustfall may be divided into a vertical dustfall component in which the dustfall adheres to a horizontal surface such as a ground surface from the upside thereof and a horizontal dustfall component in which the dustfall adheres to a vertical surface such as a wall or a window of a building from the side surface thereof. In the case of large particles such as dustfall, the vertical component and the horizontal component may be defined as the amount of the dustfall passing through an imaginary horizontal plane (in the case of the vertical flux) or an imaginary vertical plane (in the case of the horizontal flux) set in the atmosphere. The vertical dustfall component amount or the horizontal dustfall component amount may be respectively converted into the vertical flux or the horizontal dustfall flux by dividing the amount of the dustfall passing through the imaginary plane by the passage time and the imaginary area.
As a method of directly measuring the horizontal dustfall component amount, there are two types, a horizontal dustfall component trap method and a uniform suction method.
The horizontal dustfall component trap method which is a first method of directly measuring the horizontal dustfall component will be described. In this method, the external air inlet of the dust sampling port is disposed to be substantially perpendicular to the horizontal plane. The wind present in the external air is naturally introduced from the external air inlet of the dust sampling port together with the dustfall in the external air. Next, the dustfall is separated from the external air inside the dust sampling port so as to be trapped in the trap container connected to the dust sampling port. Furthermore, the dustfall trapped in the trap container is collected and the mass thereof is measured. From this result, the trapped dustfall amount per hour is obtained. The horizontal dustfall flux is calculated from the trapped dustfall amount and the opening area of the dust sampling port.
In general, since a device of this method does not need a power mechanism or a control mechanism, the configuration of the device is simple. In order to accurately trap the horizontal dustfall component, an ideal structure may be supposed as follows: in the horizontal dustfall component trap, the external air inlet is made to be perpendicular to the wind direction of the external air; the atmosphere introduction flow speed of the external air inlet is made to be substantially equal to the wind speed of the external air; and the dustfall flowing into the dust sampling port is separated from the atmosphere flowing out from the device as much as possible so as to be stored inside the device. The horizontal dustfall component indicates a horizontal movement flow of the dustfall due to the wind in the external air. The amount of the horizontal dustfall component trapped per hour and for each opening area of the external air inlet is the horizontal dustfall amount flux.
Likewise, in the ideal horizontal dustfall component trap, the trapped horizontal dustfall component amount is proportional to the horizontal dustfall flux amount at the trap position at all times. For this reason, wind speed information is not necessary when obtaining the horizontal dustfall flux amount, and the structure of the device and the analysis method may be simplified. This point is a great benefit of the horizontal dustfall component trap method compared to the other measurement methods requiring local wind speed information.
However, such an ideal horizontal dustfall component trap is hypothetical, and it is difficult to satisfy all the above-described conditions for realizing the ideal horizontal dustfall component trap in the actual horizontal dustfall component trap. For this reason, in the actual horizontal dustfall component trap, the horizontal dustfall component trap amount becomes a value smaller than the ideal horizontal dustfall component amount converted from the local and actual horizontal dustfall amount flux.
The ratio of the horizontal dustfall component trap amount of a specific horizontal dustfall component trap with respect to the ideal horizontal dustfall component trap amount is called dustfall trapping efficiency. The dustfall trapping efficiency for each device may be obtained by an experiment. In this case, the mass of the dustfall may be measured by the gauge and the measurement value may be corrected by using the dustfall trapping efficiency. Accordingly, even when the dustfall trapping efficiency of the gauge is not 100%, the horizontal dustfall flux may be highly precisely obtained through the measurement using the horizontal dustfall component trap. Further, when only the relative relationship between the horizontal dustfall amount flux at a plurality of points and time points is taken into consideration, the ideal horizontal dustfall component trap amount does not need to be essentially considered. In this case, the ratio of the actual horizontal dustfall component trap amount with respect to the predetermined standard trap amount may be obtained, and this value may be used to manage the tendency of the horizontal dustfall flux.
Even in the method of using the horizontal dustfall component trap, the benefit, in which the tendency of the horizontal dustfall amount flux is measured without the local wind speed information, of the horizontal dustfall component trap method is not basically degraded. However, in the case of the trap having low dustfall trapping efficiency, the device needs to be increased in size in order to obtain the mass of the dustfall minimally necessary for measuring the mass determined by the mass measurement method. Further, in the case of the trap of which the dustfall trapping efficiency largely changes due to the weather condition, since it is difficult to highly precisely perform correction when obtaining the horizontal dustfall flux, the measurement precision degrades. Therefore, in the horizontal dustfall component trap, the dustfall trapping efficiency needs to be high and stable. Hereinafter, the type of the specific horizontal dustfall component trap will be described.
As the trap for the horizontal dustfall flux, a device is disclosed in which wind naturally circulates inside a dust sampling port, a part of dustfall contained in the introduced wind is trapped by inertia or gravity to trap the dustfall, and a horizontal dustfall flux is measured according to the result. As this type, Non-patent Document 1 discloses a plurality of particle traps. As a representative type, a big spring number eight (BSNE) is shown in FIGS. 2A and 2B.
In the BSNE, the atmosphere naturally flowing from an external air inlet 10 into the dust sampling port 1 is decelerated inside the device as the passage is widened. Subsequently, as depicted by a flow line of an atmospheric flow 17 passing through the dust sampling port, the atmosphere naturally flows outward from an exhaust port 8 as a metallic mesh provided on the top surface of the device. The wind decelerates inside the dust sampling port, so that the staying time of the dustfall inside the dust sampling port 1 increases, and the dustfall freely falls by a long distance inside the dust sampling port in the meantime. Likewise, since the wind speed inside the dust sampling port becomes slower than the wind speed of the flow 15 of the external air, the staying time of the dustfall inside the dust sampling port 1 increases. As described above, the portion inside the dust sampling port 1 exhibiting an effect of increasing the falling distance of the dustfall may be called a wind reduction area 13. The atmospheric dustfall freely falling in the wind reduction area 13 freely falls or collides with the wall of the downstream end of the device when passing through the inside of the device as depicted by the flow line of the trapped dustfall 19, and passes through the metallic mesh 30 provided below the passage to be deposited and trapped in a particle trap 44.
A part of the dust inside the dust sampling port 1 flows into the external air from the exhaust port 8 as depicted by the flow line of dustfall 20 passing through the dust sampling port. Further, the entire device is rotatable in the horizontal direction, and the external air sampling port 10 is made to be automatically directed toward the upward wind direction at all times due to the action of a blade 23 and a rotary shaft 24 provided in the device. Since this device includes a mechanism automatically turning the external air inlet 10 in accordance with the wind direction, there is a problem in that the structure becomes complex and tends to increase in size as the horizontal dustfall component trap. Further, in this device, since the dustfall may not be always efficiently separated from the atmosphere inside the dust sampling port 1, as disclosed in Non-patent Document 1, the dustfall trapping efficiency is not high.
Non-patent Document 1 introduces a suspended sediment trap (SUSTRA) or a Modified Wilson & Cooke sampler (MWAC) as the trap for the horizontal dustfall flux. The trap principle of the SUSTRA is basically the same as that of the BSNE. The MWAC dust sampler shown in FIGS. 7A and 7B includes: a trap bottle with an external air inlet 10 which is an L-shaped pipe having an opening provided in the upward wind direction; and an exhaust port 8 which is an L-shaped pipe having an opening provided in the downward wind direction. The MWAC does not have a special mechanism that makes the external air inlet 10 of the dust sampling port follow the wind direction. For this reason, this is not suitable for a trap that traps the horizontal dustfall component for a long time in the external air of which the wind direction and the wind speed change all the time.
The uniform suction method which is a second method of directly measuring the horizontal dustfall component will be described.
In this method, the instant wind direction and the instant wind speed are measured. Further, the external air inlet of the dust sampling port is made to be perpendicular to the wind direction in the horizontal plane at all times. Furthermore, in the external air inlet, the external air containing the dustfall is suctioned at the same speed as that of the wind speed of the external air. Furthermore, the suctioned atmospheric dustfall is trapped by a trap filter or the like. As a result, the mass of the dustfall trapped per hour is measured, and the horizontal dustfall flux including the measurement value and the opening area of the external air inlet is calculated. In the case of realizing this method, generally, a device includes a power mechanism and a control mechanism suctioning the external air and changing the direction of the external air inlet.
Next, the principle of measuring the horizontal dustfall flux using the uniform suction method will be described. Generally, the dustfall which includes large particles does not completely follow the flow of the wind. In the dust sampling port 1 of the dustfall amount measurement device, the suction may be performed in the direction different from the wind direction as shown in FIG. 3 or the suction may be performed at a speed different from the wind speed as shown in FIG. 4. In such a case, it is not limited to a case in which the dustfall in the external air is suctioned to the dust sampling port 1 together with suctioned atmosphere 16. As in the dustfall 18 in the external air of FIGS. 3 and 4, the ratio of the dustfall bypassing the external air inlet 10 is too large to be ignored. Furthermore, the ratio of the bypassing dustfall is sensitively influenced by various weather conditions, characteristics of the dustfall, and the shape of the device. For this reason, it is difficult to predict the ratio of the bypassing dustfall. Therefore, the suction type shown in FIGS. 3 and 4 is not desirable as the dustfall trap method for measuring the horizontal dustfall flux. Specifically, such a dustfall sampling method is shown in Patent Documents 1, 2, and the like. In these devices, since the external air suction speed is constant in the external air inlet 10 at all times, the wind speed of the external air is generally not equal to the external air introduction speed. Further, the direction of disposing the external air inlet 10 is generally fixed in many cases. Therefore, the normally changing wind direction of the external air is not generally equal to the direction of the external air inlet 10. For this reason, as disclosed in Non-patent Document 4, the dust trapping efficiency of the particle (that is, a particle which is equal in size to the dustfall) having a diameter more than 10 μm in this type of dust sampling port 1 is extremely small so as to be several % or less. Further, since the dust trapping efficiency is strongly influenced by the ambient measurement condition such as a wind speed, it is difficult to highly precisely recognize the outdoor dust trapping efficiency. For this reason, in the external air inlet 10 of the dust sampling port 1 trapping the atmospheric dustfall in order to measure the horizontal dustfall flux, there is a need to provide a method of introducing atmosphere at substantially the same speed as the wind speed and the wind direction of the external air, that is, a uniform suction method.
As a specific example of the uniform suction method, a method is disclosed in Patent Document 2. A structure of a device using this method will be described by referring to FIG. 16. External air containing dustfall is suctioned from the external air inlet 10 using a blower or a compressor 7, and only the dustfall is trapped by a trap filter 35. The atmosphere obtained by removing the dustfall is discharged to the outside of the system from the exhaust port 8. The atmosphere containing the dustfall is suctioned to the dust sampling port 1 in a manner such that the wind speed of the external air is measured by an aerovane 31 and the suction flow rate of the blower or the compressor 7 is controlled so that the atmosphere introduction speed at the inlet of the dust sampling port 1 is equal to the wind speed at all times. The uniform suction is mainly applied when measuring the flux of the dustfall inside a gas duct of which the wind direction is fixed. In order to recognize the horizontal dustfall flux, the wind speed is controlled when applying the uniform suction to the dustfall trap at the outdoor place, and further the direction of the dust sampling port 1 is controlled so that it is aligned with the wind direction at all times. This method is disclosed in Patent Documents 4 and 5. Such a method is the most reliable method of trapping the dustfall in relation to the horizontal flux measurement.
However, in this case, the configuration and the control of the device become complex, and the device may easily become expensive and increased in size. For this reason, this may be mentioned as a simple measurement method.
Further, a low volume sampler shown in Non-patent Document 3 or a high volume sampler obtained by increasing the suction flow rate of the low volume sampler is combined with a separate aerovane, and the direction of the external air inlet and the suction flow speed may be manually corrected at all times, which may be applied in principle to the uniform suction. In this device, the suctioned atmospheric dustfall is filtered by a filter, and a change in weight of the filter is measured off-line so as to calculate the mass of the trapped dustfall. However, with this type, since an operator needs to continuously operate the device, this type is not practical as a method of measuring the horizontal dustfall flux for a long period of time.
Further, in a case where the purpose is the opposite of that of the trapping of the dustfall, that is, in a case where a suspended particulate matter (SPM) which is a minute atmospheric particle (for example, with a diameter of 10 μm or less) is desired to be separated from the dustfall to be trapped, it is desirable to adopt a dust sampling port structure in which the uniform suction state occurs as little as possible. From this viewpoint, in the case of an available SPM measurement device suctioning the external air and measuring the concentration of the SPM in the atmosphere, in order to suppress the suction of the dustfall, a dust sampling port having a shape shown in FIGS. 6A and 6B disclosed in Patent Document 3 may be adopted. The dust sampling port of FIGS. 6A and 6B includes a structure 14 that disturbs the flow inside the dust sampling port in order to suction a large particle to the air port 9 as the SPM close to 10 μm. The dust sampling port is provided on the assumption that the port is applied to an SPM measurement device used for a measurement subject which is a particle having a diameter of 10 μm or less. For this reason, the trapping of the dustfall which is a particle having a diameter more than 10 μm is not considered. For this reason, most of the dustfall flowing into the dust sampling port is directly discharged to the outside of the system through a path denoted by the reference numeral 20 in the drawing. As a result, in the case of the dust sampling port with this shape, the dustfall trapping efficiency is extremely low so as to be 5% or less as shown in Non-patent Document 4. Therefore, this shape is not suitable for collecting the dustfall.
Next, wet deposit and dry deposit of the dustfall will be described. As a physical mechanism used for when the particle of the dustfall is deposited on the ground surface or the wall surface, there are two types, that is, dry deposition of depositing only the particle of the dustfall and wet deposition of depositing the particle of the dustfall received by rain together with a raindrop. The dustfall trapped in the case of rain may be largely classified as a wet deposit, and the dustfall deposited in the case of no rain may be largely classified as a dry deposit. Even in the dustfall of the same type and size, the influence on the environment or the scattering range from the dustfall generating source is different depending on whether it is the dry deposit or the wet deposit, and there is a demand for separating the dustfall into the dry deposit and the wet deposit and trapping in this state from the viewpoint of the environmental management.
Further, the dustfall may be classified from the viewpoint of water solubility, and may be divided into soluble dustfall and insoluble dustfall. In the soluble dustfall and the insoluble dustfall, the main components of the dustfall are different from each other, so that there is a difference in environmental influence. For this reason, in the public administration, the dustfall is managed generally for each of the separate two. Therefore, the dustfall may be classified into four types, that is, dry soluble deposit, dry insoluble deposit, wet soluble deposit, and wet insoluble deposit. In accordance with the classification, it is desirable to trap the dustfall from the viewpoint of the management of the dustfall.
In the vertical dustfall component trap, as a method of realizing the four types of classification, a precipitation sampler with a structure shown in FIG. 5 is available in the market. In this device, a wet deposit dust sampling port 38 and a dry deposit dust sampling port 39 are provided above a wet deposit trap container 36 and a dry deposit trap container 37, and a dust sampling port cover 40, a cover opening and closing mechanism, a cover opening and closing control device 41, a rain detector 42, and a device protection casing 43 are provided above the sampling ports. When the rain detector 42 detects rainfall in the case of rain, the cover opening and closing control device operates the cover opening and closing device so that the dry deposit dust sampling port 39 is blocked by the dust sampling port cover 40. At this time, the wet deposit dust sampling port 38 is opened to the external air, and the dustfall as a wet deposit falls and flows into the wet deposit dust sampling port 38 together with raindrops so as to be trapped in the wet deposit trap container 36. In the case of no rainfall, the dustfall as a dry deposit is trapped in the dry deposit trap container 37 by opening and closing the dust sampling port cover 40 in the sequence opposite to the above-described sequence. In the case of this device, since a sensor such as a rain detector or an opening and closing control device is needed, the structure is complex and power is needed. Further, since the rainfall does not flow into a dry deposit sampling port 1 as not in the deposit gauge, the particle adhering to the inner surface of the dust sampling port is not cleaned to be dropped into the container bottom, and there is a problem in that the dry deposit trap amount significantly reduces since the dry deposits fly again due to wind blowing when opening the dust sampling port cover 40.
On the other hand, in the horizontal dustfall component trap, the dustfall may be trapped regardless of the presence of the rainfall. However, a device that traps the horizontal dustfall component on the basis of the presence of the rainfall as in the rain sampler was not present in the past. When the particle sampling port and the exhaust port are made to be opened and closed by detecting rainfall in the same manner as the rainfall sampler, in principle, it is considered that the horizontal dustfall component becoming wet deposit and dry deposit may be separately trapped. However, as shown in the BSNE, the horizontal dustfall component trap rotates the dust sampling port in accordance with the wind direction in many cases. For this reason, when the cover opening and closing mechanism or the measurement control device are further provided, the device and the control becomes more complicated than the rainfall sampler, which may not be considered as an efficient method. Further, in the horizontal dustfall component trapping device trapping the dustfall using an air filter such as a high volume sampler through the uniform suction method or the like, when raindrops adhere to the filter in the case of strong rainfall, an air suction resistance of the filter rapidly increases, so that a problem arises in that it is difficult to continue the suction. For this reason, such a trapping device is not actually suitable for trapping the wet deposit.
In the component analysis for a minute amount of dustfall, for example, as shown in Non-patent Document 5, generally, an ion chromatography method using an available ion chromatography analysis device or an available fluorescent X-ray method using an available fluorescent X-ray analysis device is used.